The primary objective of this study is to determine differential social reactions between neighbors and strangers in a wild population of rodents. The species to be studied was chosen because its relatively stable population size, and home range distribution indicate the probable presence of a stable social organization involving individual recognition. While no territorial behavior has definitely been observed, inferential evidence for mutual avoidance exists. In laboratory born animals we have found differential social reactions between neighbors and strangers. Populations of wild animals will be trapped to determine spatial distribution. Individuals will then be removed to the laboratory and tested against individual animals with adjoining ranges (neighbors) or stranger animals (from distant areas). Measurers of interaction will include distance maintained between animals in a large arena, approaches, latency to contact each other, type of contacts, aggressive interactions, and the time sequence of interactions. Experiments will be carried out from beginning to end of the breeding season and both intra- and inter-sexual interactions will be observed. These data will indicate the types of local-level social interactions within an organized population, the relationships within and between the sexes, and possible mechanisms of spacing within a natural population. The results of this investigation can later be used to study the population organization on a level higher than the local level, possible mechanisms of population density control, and communication within populations.